This invention relates to the treatment of carbon fibre and in particular to a method of treating the surface of carbon fibre.
Carbon fibre is conventionally produced by subjecting an organic polymer fibre to various conditions of temperature and atmosphere. Thus, for example, polyacrylonitrile fibre may be heated at a temperature in the range 200.degree. to 300.degree. C. in an oxidising atmosphere and subsequently heated at a temperature of at least 1000.degree. C. in an inert atmosphere to give carbon fibre.
Carbon fibre which is so produced is characterized by high breaking strain and Youngs modulus. Indeed such fibres are commonly incorporated in a resin matrix to provide a composite material having both strength and lightness.
In order to increase the strength of carbon fibre, it is known, for instance from British Patent No. 1,214,807, to subject the fibre to a surface removal step whereby the surface layer of the fibre is removed together with any flaws therein. Such surface removal may be achieved by various alternative methods such as ion bombardment oxidation and surface dissolution.
Whilst such treated carbon fibre is stronger than untreated carbon fibre, it has been reported (K. Morita, H. Miyachi, K. Kobori and I. Matsubara International Carbon Conference, Baden-Baden 1976) that when the treated fibre is incorporated in a resin matrix the resulting composite material is inferior to similar composite materials produced from untreated fibre. In particular, composite materials produced from the treated fibre tend to be more brittle than those produced from untreated fibre. Generally, therefore, it is apparent that the superior strength characteristics of the treated carbon fibre are not being transferred to the composite material in which they are incorporated.